Mobile subscribers are able to move freely with their mobile stations even beyond the network boundaries of their home mobile radio network (roaming). However, when a subscriber is roaming into another visited mobile radio network, he cannot easily use call numbers well known to him from his home mobile radio network such as, for example, service numbers, hotline number, mailbox number, etc. since he is subject to the numbering plan applicable in the network. Even if, in principle, it is possible to reach the call number in the other network, the mobile subscriber usually dials the call number known to him from his network in order to initiate the call. However, this procedure is unsuccessful so the mobile subscriber must take elaborate additional measures.
It is known that mobile communication systems use one or more subscriber databases (home location registers), in which the subscriber data are in each case located in their area of responsibility because of their current location.